Sheriff was a title usually used by law enforcement officers.
Bat Masterson was the sheriff of Tombstone, Arizona. In October 1881, he and Wyatt Earp rescued Steven Taylor from the Clantons. He later deputised the First Doctor to talk the Clantons out of fighting. (TV: The Gunfighters)
During the 22nd century Dalek occupation of Earth, human sheriffs were converted into Robomen by the Daleks. The Fifth Doctor and Nyssa encountered converted sheriffs in Kansas in 2158. (AUDIO: The Mutant Phase)